Remote alarm system with scanning by tones



June 14, 1966 Filed July 5, 1965 T. SALTZBERG ET AL REMOTE ALARM SYSTEM WITH SCANNING BY TONES '7 Sheets-Sheet 1 I T/M/VSL.

| T I M 1-I I l 2, 57 I +2 WW W l I FHOGIRAMMEH ggfi I 1 l2 DISPLAY I 00mm \d J L I I 7 ALARM I I mus. REC TIMIVSLATOR INPUT I I I I /0 I I u/v m5 LINE 00mm comm COUPLE/PI I I 9 M M I I TRANSL. mm. mm. I mm mm HI I ALARM //VPl/T$ I MI N I I I I H6 1 I- L/Nf M5 M5 L/NE I COUPLER COUPLER 00mm comm I 1 I 7 I I 7 I THANSL. IRA/75L mam. I I 1 IIIIIII III I III,

ALA/7M Wars I may sum/7y couwrm I FROM /4 STAGE BINARY COUNTER 5/45 POTENTIAL 3 07? MORE 0r /4 GATE I IN VENTORS Theodore Sa/fzberg Char/es H W/l/yard June 14, 1966 T. SALTZBERG ETAL 3,256,517

REMOTE ALARM SYSTEM WITH SCANNING BY TUNES Filed July 5, 1963 7 Sheets-Sheet 2 E555 k wwmfiwm 523 c M Q Ra a 5 Q s SE5 8 d R l E v EG E M 8 J QM J E L r 55:8 5% m E3 95m 55 58 2% Se i mm {L8 mm mm mfiflw vqm K E @1 g LE??? Nv L L w w @558 $.25 ESQ E v 2 6 2 E mm A was: as v m me n mmEulfiwq mm 1 5% 5% E3 23 L A. G 8 35 8 53 5 m HE" E? MEG .fi r 2.. SE 2am Q3 9% F. 6 mm 355 llll H m a 2% :3 8 g SE n f ESE GHQ QINL m fla J Q Q 8 u k N E5. d 2; E5 (mm E3 =86 m mzE m? A| A 25: K a; ru E5: 4 is =5 E I 3 an 4: t Km 8 War 6 T. SALTZBERG ET AL 3,256,517

REMOTE ALARM SYSTEM WITH SCANNING BY TONES Filed July 5, 1963 June 14, 1966 '7 Sheets-Sheet 3 mNN xmgima Q52 853w ALARM INPUTS INVENTORS Theodore Sa/fzberg BY Char/es h. Wil/mrd.

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HMQ m was H MQ q q NEE 9N MQQK June 14, 1966 T. SALTZBERG ET REMOTE ALARM SYSTEM WITH SCANNING BY TONES Filed July 5, 1963 FIG 7 7 Sheets-Sheet 4 a4 AMI? our 307 70 05c. nvpur R50,

SHIFT INPUT 0/? 0500050 224 ourpur 30 M5 MO/VOSTABLE 220 00 M5 MONOSTABLE 227 I00 M5 MONOSTABLE 220 BISTABLE RESET INVENTORS Theodore Sa/fzberg BY3 Charles H. VII/yard.

June 14, 1966 T. SALTZBERG ET 3,256,517

REMOTE ALARM SYSTEM WITH SCANNING BY TUNES Filed July 5, 1963 '7 Sheets-Sheet 5 BISTA BLES AND TONE A FILTER 056.

FIG. 6

TONE C TONE B FILTER 05C. FILTER 05C.

TONE 0 INVENTORS Theodore Sal/zberg BY Char/es Wi/Mzrd.

27(Md M June 14, 1966 'r. SALTZBERG ET AL 3,

REMOTE ALARM SYSTEM WITH SCANNING BY TUNES Filed July 5, 1963 7 Sheets-Sheet 6 June 14, 1966 'r. SALTZBERG ET AL 3,256,517

REMOTE ALARM SYSTEM WITH SCANNING BY TONES Filed July 5, 1963 '7 Sheets-Sheet 7 mmokuuc United States Patent 3,256,517 REMOTE ALARM SYSTEM WITH SCANNING BY TONES Theodore Saltzberg, Chicago, and Charles H. Wiilyarrl, Wheaten, 111., assignors to Motorola, Inc., Franklin Park, 111., a corporation of Illinois Filed July 3, 1963, Ser. No. 292,690 11 Claims. (Cl. 340-226) This invention relates to a status reporting system and in particular to a system in which the operation of remotely located alarms is indicated at a central station.

It is desirable that a large number of remotely located alarms, such as fire and burglar alarms, be capable of being monitored at a central location. This has been accomplished by using wire lines to transmit information between remotely located alarms and the central station. However, when the remote alarms are located at great distances from the central station the cost of wire lines becomes prohibitive. The use of radio links between the remote points and the central station is desirable, but has been of little use because a large number of channels have been required and the system is subject to false operation because of disturbances present in the atmosphere. The use of a radio system for transmission of information over short distances has not been practical because the cost of the terminal equipment is high compared with the cost of wire lines.

It is therefore an object of this invention to provide a system whereby the operation of remotely located alarms may be monitored from a central station and a single transmission channel can be used for a plurality of alarms.

A further object is to provide an alarm system operable over a single transmission channel which can be a wire line or a radio link or a combination of these forms of paths.

Another object of this invention is to provide a system having security against false operation for monitoring remotely located alarms.

A still further object of this invention is to provide a system for monitoring remotely located alarms at a central station which will indicate the status of the remote terminal equipment used to transmit the alarm status.

Another object of this invention is to provide a system for monitoring, at a central station, remotely located alarms whereby the remote alarms can be tested and reset from the central station.

A feature of this invention is the provision of an alarm system wherein tone groups comprised of a combination of tones are transmitted in a sequence so that the combination of tones in each group is different from that of any other group and constitutes 'an address for a particular combination of alarms at a remote location.

Another feature of this invention is the use of each tone of the combination of tones forming a tone group to indicate the status of a particular alarm at the remote location for which the group of tones is an address.

A further feature of this invention is the provision of equipment at remote locations for retransmission of the combination of tones forming the group to the central station to indicate the status of the alarms at the remote location.

Another feature of this invention is the use of groups of tones wherein one or more of the tones retransmitted to the central station are shifted in frequency if one or more of the alarms at the remote location, to which the group has been addressed, is actuated.

Another feature of this invention is the use of the duration of transmission of the group of tones to control the alarms at the remote location.

A further feature of this invention is the provision Patented June 14, 1966 of equipment at the remote location for including an extra tone in the group of tones retransmitted to the central station to indicate the status of the terminal equipment at the remote location.

Another feature of this invention is the provision of equipment at the remote location for including an extra tone in the group of tones retransmitted to the central station to indicate a failure at the remote location, such as power supply failure.

The invention is illustrated in the drawings in which:

FIG. 1 is a block diagram of the system;

FIG. 2 is a block diagram of the equipment located at the central station;

FIG. 3 is a schematic illustrating the operation of the analog AND gates shown in FIG. 2;

FIG. 4 is a block diagram illustrating the operation of the equipment at the remote location;

FIG. 5 is a time diagram illustrating the sequence of operation of the equipment shown in FIG. 4;

FIG. 6 is a block diagram illustrating the operation of the alarm logic network shown in FIG. 4;

FIG. 7 is a schematic illustrating the filter/oscillator shown in FIG. 4;

FIG. 8 is a block diagram illustrating the operation of the verification circuit shown in FIG. 2;

FIG. 9 is a perspective view of the control and display console; and

FIG. 10 is a block diagram showing the operation of the control and display console.

In practicing this invention a system is provided for determining the status of alarms at remote locations by monitoring the same from a central location by transmitting interrogations to the remote locations in sequence. The interrogation can be transmitted to the remote locations -by wire lines, by radio, or by a combination of these methods. The interrogation consists of a group of tones of diiferent frequencies, for example three tones, transmitted simultaneously. These groups of tones are transmitted in sequence by the central station equipment, with each group having a dilferent combination of tones and corresponding to a different combination of alarms located at remote locations.

Terminal equipment at the remote locations responds only to the group of tones comprising its address. When this particular group of tones is received the terminal equipment at the remote location responds by retransmitting to the central station the same group of tones, if none of the alarms at the remotelocation have been actuated. Each of the single tones in the group of tones transmitted corresponds to a particular alarm function at the remote location to which it is addressed. If the alarm function corresponding to a particular tone of the address group has been actuated this tone is shifted in frequency and the shifted tone is retransmitted as part of the tone group in place of the normal tone of that group. At the central station the retransmitted tone group is examined andv compared with the transmitted tone group, to verify the reception of a correct response, and the information contained therein is displayed. At the end of this sequence of operation another tone group is generated and transmitted to another remote location. This interrogation procedure is repeated continuously.

Referring to the drawings, FIG. 1 shows a block diagram of this system. The central station 1 includes a programmer 2, a display console 3, a radio transmitter and receiver 5 and an antenna 6. Where the remote alarms are relatively close to the central station, such plers 10.

Where the alarms are located at a considerable distance from the central station, such as alarm group 11, the information is transmitted by a radio link. A translator 9 receives the alarm inputs and transmits this information by means of transmitter and receiver 12 and antenna -14. Alarm group .15 is comprised of a number of alarms located in close proximity to each other but at a considerable distance from the central station. In order to economize on terminal equipment these alarms are tied together by wire line-s connected to. a single transmitter and receiver .16 -for transmission to the central station by a radio link. This combines the cost advantages of using wire lines for short distances and radio transmission for long distances.

Generation and transmission of a tone group FIG. 2 is a block diagram of the central station equipment used in this system. in the system described in this example, the groups of tones used as address groups are comprised of three tones selected in various combinations from 14 tones. It can be seen however, that the system is not limited to this combination of tones.

The tone oscillator 20 t as oscillator circuits [for generating 14 separate audio tones. These tones are designated A, -B, C, to N. Each of the tones generated by tone oscillator 20 is coupled to an AND gate. Fourteen separate AlND gates, represented by AND gates 25, 26, 27 and 28, control each of the separate tones from tone oscillator 20. The other inputs to AND gates 25, 26, '27 and 28 are derived from a 114 place binary counter 29, through AND gates 30, 31, 32 and 33. In this system AND gates 25, 26, 27 and 28 represent 14 AND gates and AND gates 30, 31, 32 and 33 represent 14 AND gates.

Counter 29 is a standard 14 place binary counter, each binary place having a register capable of assuming a or a 1 condition. Each of the binary places is coupled to a separate AND gate, represented by AND gates 30, 31, 32 and 33, so that when .a particular binary register is in its 1 condition the AND gate to which it is connected receives an enabling signal. When that binary register is in its zero condition the AND .gate to which it is connected does not receive an enabling pulse from the counter 29. The other input to the AND gates '30, 31, 32 and 33 is received from the output of bistable multivibrator 40.

There are 28 additional outputs, represented by output lines 41, from the '14 place binary counter 29. Each of the individual lines represents the output from one binary place and would consist of a pair of wires. One wire of the pair has an output when the binary register, to which it is connected, is in its 1 condition while the other wire has an output when the binary register to which it is connected is in its 0 condition. Each of the registers of the 14 place binary counter is given the letter designation of tone oscillator which it controls. For example, when the binary register controlling tone A is in its 1 condition it would be given the designation A and when it is in its 0 condition it would be given the designation K. This designation holds for all the binary registers. The line 41 having an output when binary register A is in its 1 condition is designated A, while the line 41 having an output when binary register A is in its 0 condition is designated K The cable designated by the number .2 includes a group of 28 separate lines comprised of A B,, C, through N, and K E, 6, through i These lines are connected to the control :and display console and the verification circuit through lines '43, 44 and 45. Lines 48, 49 and 50 are comprised of only 14 of the 28 wires in the cable 42. These wires carry the information A,, B,, C, through N and are applied \through cable 48 to ANALOG AND gate 51 and ANALOG AND gate 52. The detailed operation of ANALOG AND gates 51 and 52 is described in detail in a subsequent portion of this specification.

As :the binary counter 29 counts through the entire sequence of numbers of which it is capable of counting, from 00000000000000 to 1111'11111111111, information is to which registers are in the 0 condition and which are in the 1 condition is transmitted over cables 42, 48, 49 and 50 to the ANALOG AND gates 51 and 52. Whenever the binary number held in :the registers of binary counter 29 has three or more places containing a 1 the ANALOG AND gate 52 produces 13.11 output which turns on AND gate 53. Whenever this binary number has four or more places containing a 1 the ANALOG AND gate 5-1 produces an output which inhibits the AND gate 53. Thus AND gate 53 will have an output whenever the 14 place binary counter has at least three but less ltllall four 1s in its binary register. AND gate 53 will produce an output only when there are three 'and only three registers of the counter 29 which contain a 1. The three registers containing ls will each send an enabling signal to the appropriate AND gates represented by AND gates 30, 3 1, 32 and 33.

Fast clock 56 (at the upper left corner of FIG. 2) produces output pulses at a frequency of approximately 16 kilocycles per second. These pulses are coupled to counter 29 through AND gate 57. Each pulse causes the number contained in counter 29 to increase by one. AND gate 57 is enabled by the output from bistable multivibrator 53, which is normally in state 1.

AND gate 59 receives an input from AND gate 53, and a second input irom the control and display console 73 over line 60. This signal comes from AND gate 447, located in the control and display console, over the recognized address bus as shown in FIG. 10. The input signal on line 60 normally enables AND gate 59 and its derivation will be described in a subsequent portion or this specification. When an enabling signal is received by AND gate '59 from AND gate 53, an output signal from AND gate 59 is coupled to bistable 'multivibrator 58 causing multivibrator '58 to assume its second stable state. When this occurs the enabling signal from state 1 of multivibrator 58 is no longer applied to AND gate 57 and the pulse from fast clock 56 does not reach the counter 29. The counter 29 will remain at the number which it has stored in its registers until multivibrator 58 returns to its first stable state. 1

Reviewing the operation of this circuit, counter 29 counts through a sequence of numbers from 0 to 11111111111111 at a rate controlled by fast clock 56. When 3 and only 3 of the registers of counter 29 contain a 1 this is sensed by AND gates 51 and 52. A signal is developed which prevents the signal from fast clock 56 from reaching counter 29 so that the counter will stop at this position. The output signals from the three registers of counter 29 which contain a 1 are used to enable 3 of the 14 AND gates represented by AND gates 25, 26, 27 and 28 for selecting three tones from the 14 tone oscillator 20. The time during which these enabling pulses are applied to the AND gates controlling the tone outputs is determined by an input signal to AND gates 30, 31, 32 and 33 from multivibrator 40.

When a pulse is applied to multivibrator 58 from AND gate 59 the multivibrator is shifted from its number 1 state to its number 2 state. At this time the output from the number 1 state of the multivibrator is removed from AND gate 57 causing counter 29 to stop. At the same V time multivibrator 58 produces an output signal which is applied to ring counter 66 and AND gate 63. This signal resets ring counter 66 to the zero position to insure that the counter will operate through the proper sequence. When this signal is applied to AND gate 63, an output is produced in the event that inhibiting inputs are not applied to the remaining two inputs of AND gate 63. The output of AND gate 63 is applied to AND gate 64 enabling this gate and permitting pulses from slow clock 65 to be applied to ring counter 66.

The pulses applied to ring counter 66 cause this counter to step through a sequence of operations from one through ten and back to zero. At count one, bistable multivibrator 40 is shifted to its second stable state and produces an output signal which is applied to the AND gates 30, 31, 32 and 33 enabling these gates. An output signal is developed from 3 of the 14 AND gates represented by AND gates 30, 31, 32, and 33, which are connected to three registers of counter 29 which are in a 1 condition. These three output signals are applied to three of the 14 AND gates represented by AND gates 25, 26, 27, and 28 thus permitting tones from oscillator 14 to be applied to mixer 76. Since counter 29 will stop counting and actuate ring counter 66 when there are three and only three 1s contained in its registers, only three tones will be applied to the mixer 76 from tone oscillator 20. When the ring counter is stepped to count 2, bistable multivibrator 39 is shifted to its second stable state and produces an output pulse which turns on the master tone gate 77 permitting the three tones mixed in mixer 76 to be applied to modulator 78. Modulator 78 modulates a carrier frequency signal produced by transmitter 79. This signal is applied to an antenna 84 for transmission to a receiver at a remote location. It should be noted that the group of tones developed in mixer 76 can be applied to a remote location by means of a wire line as well as by radio transmission with no changes in the basic operation of the system.

When counter 66 reaches position 5, mutivibrator 39 is returned to its first stable state turning off the master tone gate 77 removing the group of tones from the transmission medium. At count 6 multivibrator 40 is returned to its first stable state removing the enabling pulses from the 14 AND gates represented by AND gates 31, 32 and 33 removing the output signals from these gates. The three of 14 AND gates represented by AND gates 25, 26, 27 and 28, which allow the tones to be applied to mixer 76 are thus disabled.

At count 6 the central station ceases transmitting the tone group to the remote location, and the receiver 80 is connected to antenna 84 to receive the reply from the re mote location. This reply is filtered in filters 82 to separate the tones which are then detected in detector 83 and applied to a verification circuit 74. During count 9 a pulse from counter 66 is applied to verification circuit 74 and a verification of the returned signal is made. At count the results of the verification are applied from the vertification circuit 74 to the control and display console 73. The operation of the verification circuit 74 and the control and display console 73 will be explained in detail in a subsequent portion of this specification. When counter 66 reaches the zero state a pulse is transmitted to multivibrator 5S returning it to its first stable state. The output of multivibrator 58 then produces the enabling pulse which turns on AND gate 57 causing counter 29 to resume its count searching for a subsequent 14 place binary number containing three and only three ls.

Generation and transmission of a test and/0r reset signal The tone group is transmitted for the time period from count 2 to count 5, which in the system described is approximately 50 milliseconds duration. By changing the length of the time during which the group of tones is transmitted, the alarms located at the remote unit can be reset and/ or tested. This is accomplished by controls located on the control and display console. If it is desired to test or reset the alarms at the remote locations, a signal is applied from the control and display console to bistable multivibrator 72 changing it to its second stable state. Multivibrator 72 then produces a signal which is applied to AND gate 70. When counter 66 reaches its second count, and the tones are applied to modulator 78 through master tone gate 77 a signal is also applied to AND gate 70. With both enabling signals present AND 6 gate 70 produces an output signal which enables AND gate 71 and inhibits AND gate 63. By inhibiting AND gate 63 counter 66 remains in its second count as the output of AND gate 63 is removed from AND gate 64 disabling this gate and preventing the application of pulses from slow clock'65 to counter 66. Pulses from slow clock 65' are also applied to AND gate 71and when this AND gate is enabled by a signal from AND gate 70,

pulses from slow clock 65 are applied to ring counter 68 which counts for a predetermined time duration. At the end of this time duration, a pulse is applied to multivibrator 72 returning it to its first stable state. The output from multivibrator 72 applied to AND gate 70 is removed causing the output signal from AND gate 70 to cease. AND gate 71 is thus disabled and AND gate 63 is enabled causing counter 66 to resume its count. From this point the sequence of operation continues as previously described. Thus a signal of a predetermined time duration but longer than the normal time duration, is applied to the equipment located at a remote location to reset the same. To test the remote equipment, a signal longer than the reset signal but of indefinite duration is used. This is generated by a control on the control and display console 73 which applies a signal over line 86 to AND gate 69 enabling this AND gate. When AND gate 66 reaches count 2 a signal from the output of count 2 is applied through AND gate 69 to AND gate 63 inhibiting this AND gate and blocking the pulses from slow clock 65 which are applied to counter 66. Counter 66 will remain in count 2 position and will continue to send out a group of tones until the output from the control and display console 73 is removed. The effect of this signal of longer than normal time duration on the receiving equipment will be described in a subsequent portion of this specification.

Analog and gates, three and only three of fourteen FIG. 3 is a schematic showing in detail AND gates 51, 52 and 53 of FIG. 2.

The operation of the three or more of fourteen AND gate 52 and the four or more of fourteen AND gate 51 is identical and the values of the components used in the two circuits can be the same with the exception of resistors 106 and 131. The values of these resistors determine the number of inputs required for the AND gate to develop an output.

Resistors 103A to 103N and 106 constitute a voltage divider network which determines the voltage applied to the base of transistor 109. Each of the registers of the counter 29 are coupled to AND gate 51 and 52 through isolating diodes 102 and104. When a register is in its 0 state a zero voltage is applied to the input of AND gate 51 and 52 to which it is connected. When a register is in its 1 state a minus voltage is applied to that input. Thus the voltage developed on the base 110 of transistor 109 when register A is the only register in the 1 state will be determined by the voltage divider comprised of resistors 103A and 106. When two of the registers, for example registers A and Bare in the 1 state the voltage on the base 110 will be determined by the voltage divider comprised of resistors 103A and 103B in parallel, in series with resistor 106. As the number of registers which are in the 1 'state increases the voltageapplied to the base 110 will decrease in steps. The emitter 112 of transistor 109 is biased at a constant voltage by means of resistor 114 and zener diode 115 connected between a negative supply voltage and ground. By proper selection of the bias voltage applied to the emitter electrode 112 and the value of resistor 106 transistor 109 can be biased to conduction when a predetermined number of registers of the counter 29 are in the 1 state. The resistors 106 and 114 and the value of zener diode 115 have been chosen so that the transistor 109 of AND gate 51 will conduct when four or more of the registers of counter 29 are in the 1 state. AND gate 52 is similar in construction to AND gate 51. Resistors 105A to 105N have the same purpose as resistors 103A to 103N and can have the same value. Resistor 138 and zener diode 139 connected between a negative supply voltage and ground furnish a bias potential for the emitter 135 of transistor 132. Resistor 131 is chosen so the bias voltage applied to the base 133 of transistor 132 will be sufiicient to bias the transistor to conduction when three or more of the inputs to the AND gate 51 have minus voltages applied, that is when three or more of the registers of counter 29 are in the 1 state.

hen the transistors 109 and 132 are not conducting the output of AND gates 51 and 52 are a minus voltage equal to the supply voltage. When these transistors conduct, resistors 113 and 137 cause the output voltage of AND gates 51 and 52 to rise due to the voltage drop across the resistors. The output of AND gate 52 with all of the registers of counter 29 in the state in a minus voltage and is applied through diode 142 and the network comprised of resistors 143 and 145 and capacitor 144 to the base 147 of transistor 146. Resistors 143 and 145 from a voltage divider network to divide down the voltage from AND gates 51 and 52 applied to transistor 146. A bias potential is supplied to the emitter from a supply 157 to provide for temperature stabilization of the circuit. The minus voltage applied to the base 147 from AND gate 52 is sufficient to cause transistor 146 to conduct. When transistor 146 conducts the voltage at terminal 154 is higher than the supply voltage because of the drop through resistor 150. The output of AND gate 51 is applied to the base 123 of transistor 122 through a network comprised of resistors 119 and 120 and capacitor 118. A bias supply for the emitter 125 of transistor 122 is supplied through resistor 127 and zener diode 128 connected between a negative supply voltage and ground. When transistor 109 is biased off transistor 122 is biased to conduction. With transistor 122 conducting the voltage at the collector 124 is higher than the supply voltage because of the voltage drop through resistor 126. This output voltage is applied to transistor 146 through diode 141. Since the voltage applied from AND gate 52 is less than the voltage applied from the collector 124 of transistor 122, diode 141 is biased so that it is nonconducting.

When three of the registers of counter 29 are in the 1 state transistor 132 is biased so that it will conduct and the voltage at the collector 134 rises due to the voltage drop through resistor 137. This voltage applied to the base of transistor 146 is no longer sufiicient to bias this transistor to conduction so that the transistor is cut off and the voltage appearing at the collector 148 and terminal 154 decreases.

When four of the registers of counter 29 are in the 1 state transistor 109 of AND gate 51 conducts causing the voltage appearing at collector 111 to rise. The voltage applied from collector 111 to the base 123 of transistor 122 is no longer sufiicient to bias this transistor to conduction so that the voltage at the collector 124 decreases. This decrease in voltage is applied through diode 141 to the base 147 of transistor 146 where it biases transistor 146 to conduction. With transistor 146 again conducting the voltage appearing at the collector 148 and terminal 154 rises. Thus the output voltage at terminal 154 will be equal to the supply voltage when three and only three of the registers of counter 29 are in the 1 state. This negative voltage is the output signal developed by AND gate 53 of FIG. 2 and applied to AND gate 59.

Operation of the remote terminal equipment FIG. 4 shows a block diagram illustrating the operation of the terminal equipment at the remote location. In the system described in this example the terminal equipment is capable of receiving alarm inputs from 12 separate alarms consisting of four groups of three alarms each. The equipment is responsive to four separate tone signals from the central station. It can be seen that the combination of four tones taken three at a time will produce four separate tone groups with each tone group having three tones. Each of the four tone groups is associated with a separate group of alarms and each tone of the tone group is associated with a separate alarm in the alarm group. The number of tones in the group is a design feature and is not limited to three as described in this example.

The signal from the central station transmitter is picked up on antenna 200 and applied to receiver 202 where it is demodulated. It should be noted that the signal from the central station could be applied to the remote terminal equipment by wire line without the use of radio transmission and without any basic difference in the operation. In the example illustrated, the remote equipment is coded to receive four tones which will be designated tone A, tone B, tone C, and tone D. The code groups associated with these tones are ABC, ABD, ACD and BCD. The tones received are applied to the filteroscillators 204, 205, 206 and 207. If the tone is of the proper frequency for the filter-oscillator to which it is applied, it will produce an output which is detected in one of the tone detectors 210, 211, 212 and 213. The operation of the filter-oscillators will be described in a subsequent portion of this specification. The output of the tone detectors are applied to address decoders 215, 21.6, 217, and 218 which are THREE INPUT AND gates which also have an inhibiting input. The address decoders will produce an output only when the three tones associated with its address are present, and there is no inhibiting pulse present. For example, if the group received was comprised of tones ABC, address decoder 215 would produce an output provided there was no inhibiting pulse present at this AND gate. The output of this gate is applied to bistable multivibrator 220 and causes this multivibrator to change to its second stable state. The output of the address decoder 215 is also applied to an OR decoder 224. Decoder 224 produces an output when any one of the address groups associated with this equipment are received.

The output from the decoder 224 is applied to the monostable multivibrators 226, 227 and 228. Monostable multivibrator 226 is triggered to its unstable state where it will remain for 30 milliseconds before returning to its stable state. During the time that the monostable multivibrator 226 is in its unstable state, it applies an inhibiting signal to the millisecond monostable multivibrator 227. By disabling the 80 millisecond timer for a period of 30 milliseconds, the system is protected against transients and disturbances which may be present and which are normally of a very short duration. Thus the signal received must contain tones of the proper frequency and must last for a predetermined time duration, in this example 30 milliseconds, before the system will recognize the tones as a proper address. The 80 millisecond timer 227 and the millisecond timer 228 are not shifted to their unstable state until the signal applied to them by the decoder 224 ceases. The timing of the monostable multivibrators 226, 227, and 228 and the output of the decoder is shown in FIG. 5.

The output of the 100 millisecond monostable multivibrator 228 is applied to the address decoders 215, 216, 217 and 218 to inhibit these decoders so that no code groups will be detected by them for 100 milliseconds after reception of the original tone group has terminated in order to prevent false operation of the terminal equipment. The output of the 80 millisecond timer is applied to various portions of the circuit in order to initiate a reply to the interrogation as to the status of the group of alarms associated with code group ABC. One of the portions of the circuit to which the output of the 80 millisecond timer 227 is applied is the alarm logic network 242 which is shown in detail in FIG. 6.

Alarm logic network Referring to FIG. 6, the 12 alarm inputs are shown numbered from 1 to 12 and are coupled to a series of bistable multivibrators which are normally set in their number 1 state. The alarms associated with code group ABC are alarms numbered 1, 2 and 3 in which alarm numher 1 is associated with tone A, alann number 2 is associated with tone B, and alarm number 3 is associated with tone C. Another example would be the alarms associated with the code group ACD, which comprise alarms.

7, 8, and 9 in which alarm 7 is associated with tone A, alarm 8 is associated with tone C and alarm 9 is associated with tone D. It can be seen that-each of the tones will have associated with it three separate alarms in difierent alarm groups, the alarm interrogated being determined by the code group of three tones which is received.

If the alarm associated with input 2 is actuated, bistable multivibrator 325 will be triggered to assume its second stable state and the output will be applied to OR gate 309. The output of the OR gate 309 is applied to an AND gate 293. An additional input to AND gate 293 is the output of the address bistable 220 of FIG. 4 which is triggered when the ABC address is received. Thus only the AND gates associated with the address received can be enabled, and if this were not done an error might arise. For example, if alarm was actuated and alarm 2 was not actuated, and if the output of alarm 5 were allowed to trigger the B tone shift when the ABC alarms were being interrogated, the central station equipment would indicate an alarm actuation of alarm 2 which would not be correct. This is prevented by allowing the AND gates 292, 293 and 294 to be actuated only when tone group ABC associated with alarms 1, 2, and 3 is received.

The third input to AND gate 293 is the output of the 80 millisecond multivibrator 227 of FIGURE 4 which enables the AND gate at the proper time in the sequence of operation. The output of AND gate 293 is coupled to the tone B filter oscillator 205 of FIGURE 4 through the shift tone B OR gate 278. This informs the filter oscillator 205 of FIGURE 4 that alarm 2 designated by tone B of the received code group consisting of tones A, B and C, has been actuated and that the tone B should be shifted in frequency. Since alarms 1 and 3 have not been actuated there is no output to filter oscillators 204 and 206 of FIGURE 4 indicating that the tones generated by these oscillators should be shifted.

(Remote terminal equipmentcont.)

Referring again to FIGURE 4, the output of the 80 millisecond timer 227 also enables the key oscillator AND gates 243, 244, 245 and 246. Since it is desired to transmit only the tones A, B, and C, in this example, an inhibting pulse is received by the key oscillator D AND gate 243 from the output of a bistable multivibrator 220 which in its number 2 state represents an input code group ABC. The outputs of key oscillator AND gates 244, 245 and 246 key the oscillators A, B, and C for the duration of the output of the 80 millisecond timer 227. The output of these oscillators are combined and applied to the transmitter 201 and transmitted to the central station either by radio or by wire line. In this case tone B associated with alarm input 2, which has been actuated, would be shifted in frequency to indicate to the central station that this alarm has been actuated.

In addition to the three tones comprising the code group, the system uses a fourth tone to indicate the condition of the terminal equipment associated with the alarms to which the three tone code group is addressed. This fourth tone is the same for any code group and in this example consists of a 240 cycle tone generated by 240 cycle generator 255. This tone is called the X function and the input generated by the monitoring devices located at the equipment'associated with code group ABC is designated X1. The X function inputs from the monitoring devices located at the equipment associated with code example, at the power supply to the alarm equipment as- 10 groups ABD, ACD, and BCD are designated X2, X3, and X4 respectively. Monitoring equipment located, for

sociated with code group ABC will produce an output signal X1 which is coupled to AND gate 49 if the power supply to this alarm equipment fails. This AND gate is enabled by the output from the multivibrator 220, and the output from the 80 millisecond timer. If there is a malfunction on the circuit being monitored, an input will be received from the terminal designated X1 enabling AND gate 249. The output of AND gate 249 is applied through OR gate 254 to AND gate 256 inhibiting the output of this gate. When there is no output from this gate the 240 cycle signal will not be present in the return signal from the remote location and this fact will be indicated at the central station.

The 80 millisecond timer pulse also turns on the transmitter at the beginning of the pulse in order to transmit only when the system is being interrogated. At the cessation of the 80 millisecond pulse, a bistable reset pulse is applied to the bistable multivibrators 220, 221, 222 and 223 resetting these multivibrators to their number one state.

As previously described, a tone signal from the central station of longer duration than normal can be used to test and/ or reset the alarms at the remote location. The output of the decoder 224 is coupled to 200 millisecond time delay 229 and 500 millisecond time delay 230. The output of the 200 millisecond time delay is coupled to reset AND gates 232, 233, 234 and 235. Other inputs of the reset AND gates 232, 233, 234 and 235 are the outputs of the address bistable multivibrators 220 through 223 and the output of the decoder. The outputs of these AND gates are coupled to bistable multivibrators 313 through 326 of FIGURE 6. If a signal is still present after a 200 millisecond time duration, the output of the 200 millisecond time delay circuit will apply an enabling pulse to the reset AND gates 232 through 235, and the AND gate enabled by the particular address decoder which is in its number two stable state will produce an output which is applied to the alarm logic network. In the example of code group ABC, the alarm reset would be applied through reset AND gate 235 to set the alarm storage bistables 323, 325 and 326 of FIG. 6 to their number 1 state.

Also shown in FIG. 4 are four test AND gates 237, 233, 239 and 240. These are actuated by the outputs of the address bistable multivibrators 220 through 223 and the output of the 500 millisecond time delay 230. If the tone signal is still being transmitted 500 milliseconds after it has first been received at the remote location, the appropriate test AND gate connected with the particular code group being transmitted will be actuated. The outputs of -these test AND gates can be used to .operate standard test equipment located at the remote location.

FIG. 7 illustrates the operationvof the filter-oscillator circuits shown as block diagrams 204, 205, 206 and 207 of FIG. 4. This circuit is capable of operating either as an oscillator or as a tuned amplifier. When operating I of 276, 277, 278 and 279 of FIG. 6.

When operating as a filter or tuned amplifier an audio input voltage is applied to terminal 351 and is developed across input resistor 352. The circuit comprised of capacitor 353 and inductance 354 forms the first section of a series tuned networth, and is tuned to the desired frequency. Capacitor 355 terminates the first tuned section for optimum frequency response and capacitor 356 couples the signal to a second series tuned section comprised of capacitors 357, 360,- 362 and 365 and inductance 358. This section is tuned to the same frequency as the first tuned section. 1

The output of the second tuned stage is coupled to the base 380 of transistor 379. The bias on the base is determined by resistors 373, 374, 378 and 386 connected between a source of negative potential and ground. Capacitor 372 is a bypass capacitor used to decouple the stage from the power supply. Diode 377 is a diode having temperature characteristics opposite to that of transistor 379 in order to compensate for the changes of transistor 100 with temperature. Resistors 335 and 386 are used to stabilize the bias of transistor 379 and resistor 385 also provides degeneration for the amplifier stage. Capacitor 369 furnishes an alternating current bypass for resistor 386. Capacitor 368 provides a feedback path from the emitter 384 of transistor 379 through resistor 385 to the base 380 of transistor 379. The output of the emitter follower, transistor 379, appears on terminal 382.

When the filter-oscillator operates as a filter, transistor 387 is inoperative as it is biased so that it is non-conducting by a ground potential applied from a key oscillator AND gate represented by blocks 243, 244, 245 and 246 of FIG. 4. This biases diode 43 so that it will conduct and the resulting voltage drop across resistor 392 causes the voltage at the base 391 of transistor 387 to rise to a point near ground potential. The potential of emitter 390 is less than the potential on the base 391 because of the voltage drop through resistor 386.

Summarizing as to the filter operation, the input voltage from terminal 351 is filtered by the two tuned circuits and applied to the base of transistor 379. The input signal is amplified in this transistor and is applied from the emitter 384 thereof to the amplifier output terminal 382. From this point it is coupled to one of the tone detectors represented by blocks 210, 211, 212 and 213 of FIG. 4.

There is a small output signal present at the oscillator output terminal 364, but this output is very low and is applied to a transmitter which is turned off and therefore it is not transmitted. The output of the emitter follower transistor 379, is in phase with the input and this output is coupled from the emitter 384 to the base 380. However, the gain of this feedback loop is not suflicient to establish transistor 379 as an oscillator because of the degeneration caused by resistor 385.

In order to change the operating condition of the filteroscillator circuit to that of an oscillator, a negative potential from the key oscillator AND gate associated with this filter-oscillator is applied to terminal 376. This biases diode 393 so that it is non-conducting and reduces the voltage drop across resistor 392 so that the voltage appearing at the base 391 of transistor 387 will decrease. This biases transistor 387 to conduction and the alternating current impedance from the collector to emitter electrodes of transistor 387 becomes low. The low impedance alternating current path from the collector 389 to the emitter 390 bypasses resistor 385 and eliminates the effects of its degeneration from the feedback path.

Two criteria are necessary for transistor 379 to oscillate. The gain of the transistor stage multiplied by the gain of the feedback path must be equal to or greater than one and the signal applied to the base 380 must have the proper phase. With the effect of the degeneration of resistor 385 removed the gain of the feedback path is increased so that the first critetion is met. If the signal applied to the base 38%) from the emitter 384 is of the same frequency as that to which the series resonant circuit, comprised of capacitors 357, 360, 362, 365 and inductance 358 is tuned, the signal will have the proper phase. The series resonant circuit will appear to be resistive at resonance and therefore there will be no phase shift through capacitor 368. As the signal at the emitter 384 has the proper phase angle for oscillation the second criterion is met and the transistor 379 will oscillate at the resonant frequency of the series circuit comprised of inductor 358 and capacitors 357, 360, 362 and 365.

If the frequency of the signal applied to base 380 from emitter 384 is different from the resonant frequency of 12 the series resonant circuit this circuit will appear reactive and the signal will undergo a phase shift. Thus the second criterion will not be met and transistor 379 will not oscillate.

Diode 367 is normally biased so that it is non-conducting by a negative voltage applied to terminal 363. When it is desired to shift the frequency to indicate that an alarm has been actuated, a positive voltage is applied to terminal 363 biasing diode 367 so that it is conducting. This effectively bypasses capacitors 360 and 362 removing them from the tuned circuit thus changing the resonant frequency of the series tuned circuit and the frequency of the oscillators to a slight degree. The output of the oscillator is taken from the junction of capacitors 360 and 362 to provide a relatively constant output level with changes in frequency. The oscillator frequency is also coupled out through terminal 351 to the preceding stage. However, this stage is the output of an amplifier and the signal is rapidly attenuated at this point. A strong oscillator signal is also coupled to terminal 382 and from there to the tone detectors represented by blocks 2'10, 211, 212, 213 of FIGURE 4 and to the address decoders represented blocks 215, 216, 217 and 218. However, when the filter oscillator is in its oscillating condition, an inhibiting pulse is applied to the address decoders from the 100 millisecond timer which prevents the oscillator output from being applied to other parts of the circuit.

Thus the amplifier oscillator circuit described in FIG. 7 can act as a tuned amplifier responsive to a single audio tone, or it can be made to act as an oscillator capable of generating the same tone or a tone shifted in frequency.

Receiving the retransmitted tone group at the central station Referring again to FIG. 2, the signal transmitted by the remote station is received by antenna 84 and receiver 80, and the tones are separated and detected in filters 82 and detectors 83. The signal could also be transmitted by wire line to the central station. In the example being discussed, the code group transmitted back would consist of code group ABC with tone B shifted. The shifted tone B is designated as B while the normal tones are designated as A and (3,. The outputs from the detectors are coupled to the verification circuit 74 over cable 85 while the X function is coupled directly to the control and dis-play console 73. Cable 85 consists of 28 separate lines each line associated with a separate detector output, that is A B N and A B N Operation of verification circuit The operation of the verification circuit is shown in FIG. 8. Each of the tones which can be transmitted has a separate stage for verification of the .presence or absence of that tone. Each of these stages is identical in operation and in FIG. 8, only three of the stages are shown. The stage for verify-ing tone A is designated as 400, the stage for verifying tone B as 401, and the stage for verifying tone N as 402. There are three groups of inputs to the verification circuit. The first group of inputs consist of 28 individual lines designated as lines 41, 42, 43 and 44 coupling the 14 place binary counter 29 to the verification circuit 74 in FIGURE 2. These 28 lines are comprised of 14 pairs, each pair of lines associated with a tone. One of the pairs of lines is energized when a tone is selected to be transmitted, the other of the pair of lines is energized when a tone is not selected to be transmitted. Thus one and only one line of each pair of lines is energized at a time. A line 'which is energized when a tone is to be transmitted is designated by the letter of the tone followed by a small subscript t for example A The line which is energized when the tone has not been transmitted is designated, for example, by an K In FIG. 8 these lines are shown for only three of the inputs A, B and N.

The second group of inputs is comprised of the received tones. These also consist of 14 pairs of inputs. One pair being associated with each tone. One of the pair of wires is energized if the tone is at the same frequency which was transmitted, while the. other line is energized if the tone is shifted in frequency indicating an alarm has been actuated. A received tone which is unshifted is designated by capital letter followedby a subscript r for example A while a tone which has been shifted in frequency will be designated by a subscript s for example A The third input is applied only to the initial verification circuit 400 and is a constant error generator input.

In the example given the tones received from the remote location would consist of A B and C The transmitted tones would consist of A B and C Thus lines A B and C, would be energized. Also lines A B C and D through N would be energized. The OR gate 404 will provide an output if either the A or the A input line is energized. This output, which in the example. given will the the A line, is applied to AND gate 405 and inverter 412. Inverter 412 changes the input signal from the OR gate 404 so that if a signal is applied to AND gate 405 from OR gate 404 no signal is applied to AND gate 406 from OR gate 404. The no error generator 407 also applies a signal input to AND gates 405 and 406. This is used to keep the circuitry of the verification circuits the same throughout the system. The K signal is applied to AND gate 406 and the A signal is applied to AND gate 405. For a verified response it is desired to have an output from either AND gate 406 or 405 but not both at the same time. In order to achieve an output from AND gate 405 it is necessary that tone A has been selected and that either A or A :be received, plus an input signal from the no error generator 407. In order to obtain an output from AND gate 406 it is necessary that no A or A signal has been received and that the A tone has not been selected, as well as receiving a signal from the no error generator 407. Since these two events are mutually exclusive a correct response will produce an output signal from AND gate 405 if tone A has been selected and an output signal from AND gate 406 if .tone'A has not been selected. The output signals from AND gate-s 406 and'405 are applied to inverters 408 and 409 and from there to AND gate 410. Because of the inverter 412 it is impossible to have an input from OR gate 404 applied to AND gates 405 and 406 simultaneously. Therefore, it will be impossible for both of these gates to have an output at the same time. This will prevent a verification signal from being generated if a signal has been received which has not been selected. If a signal is selected but not received there will be no output from either AND gate 405 or 406 and thus AND gate 410 will have inputs applied to it from inverter-s 408 and 409 and will generate an output signal. This output signal is inverted in inverter'411 and applied to AND gates 415 and 416 of the subsequent stage 401. Thus the verification circuit 400 becomes the equivalent to the no-error generator 407 for the verification circuit 401. It can be sen that if the no error generator 407 were not to apply a signal input to AND gates 405 and 406 there would the no output from inverter 411 thus indicating an error to verification circuit 401. Once an error has been established in any verification circuit the following circuit-s will always have an error for an output.

The output from verification circuit 402, the end circuit in the chain, is applied to AND gate 418 to inhibit this gate. It is also applied to ibista'ble multiv-i-rator 419. It should the noted that the output of verification circuit 402 is not inverted as the output of the other verification circuits. Therefore, if an error has been developed there will be an output signal from verification circuit 402, AND gate 418 will be inhibited and bistable multivibrator 419 will be shifted to position 2. If there has been no error detected in the verification circuit, AND

14 gate 418 will not :be inhibited and the signal from the ring counter 66 of FIGURE 2, applied at the ninth count, will establish bistable multivibrator 419 in its first stable state.

The outputs from bistable multivibrator 419 are applied to AND gates 420 and 421 as is the output [from count 10 of ring counter 66 of FIGURE 2. If the bistable multivibrator is in its first stable state the count 10 from ring counter 66 will develop an output from AND gate 420 which is the verification output. If multivibrator 419 is in its second stable state count 10 from ring counter 66 will establish an output from AND gate 421 which is the not verified state indication. The verification signal (from AND gate 420 and the not verified signal from AND gate 421 are applied to AND gates 448 and 449 respectively over lines 440 and 441 as shown in FIG. 10.

Control and display console Referring again to FIG. 2, the outputs of the verification circuit are applied to the control and display console which is illustrated in FIGS. 9 and 10.

The control and display console consists of a cabinet containing a plurality of panels 502, each panel corresponding to a separate tone group. Panel 503 shows in detail the elements contained on each of the panels. Lamps 506, 508 and 510 are the alarms corresponding .to the tones of that tone group. In the example illustrated where panel 503 represents tone group ABC, lamp 506 would represent tone A and therefore alarm number 1, lamp 508 would represent tone B and therefore alarm number 2, and lamp 510 would represent tone C and therefore alarm number 3. Switches 505, 507 and 509 are reset switches. Lamp 504 is a master lamp which will be illuminated 'whenever any of the alarms associated with this particular panel are actuated. Lam-p 512 indicates the actuation of the X function. Switch 51-1 is a three position switch. The normal operating position is the center position. Moving the switch to the right or left enables the remote set of alarms associated with this panel to be tested and/or reset. Lamp 500 is a main alarm lamp and lamp 501 is a secondary alarm lamp.

FIG. 10 is a block diagram of the panel shown in FIG. 9. The inputs to the panel are as follows: i

(a) Verified signal (v) on line 440 from AND gate 420 of FIG. 8

(b) Not verified signal (E) on line 441 from AND gate 421 of FIG. 8

(c) Tones transmitted on lines 443 (in this example three tones would be A B and C (d) X function on line 444 (e) Received signal shifted on lines 461, 462, and 463. 5 5 s)- The A B; and C inputs are applied to AND gate 447 and generate a recognized address signal which is applied to the recognized address bus. This bus is connected to AND gate 59 of FIGURE 2. The recognized address signal is also applied to AND gates 448 and 449. AND gate 449 recognizes the E signal and if there is an input on line 441 bistable multivibrator 450 is shifted to its second stable state. The output from state two of this multivibrator causes lamp 452 to be illuminated and actuates audible alarm 453 through OR gate 454. The recognized verification signal is applied on line 440 to AND gate 448. The output from AND gate 448 will shift bistable multivibrator 450 to its first stable state and also apply a signal to the tone A AND gate 455, tone B AND gate 456 and the tone C AND gate 457. The output of AND gate 448 is also applied to AND gates 464 and 465. The X function is applied to the X inverter 468 from line 444. If a signal is present on 444 an X output is applied to AND gate 464. If no signal is present on line 444 an X is generated and applied to AND gate 465. When AND gates 464 and 465 are enabled by a signal from AND gate 448 an X output from X inverter 468 will cause bistable multivibrator 469 to assume its second stable state causing lamp 478 to be illuminated and causing alarm 453 to be actuated through OR gate 454. A signal present on line 444 will cause a signal applied to AND gate 464 to reset bistable multivibrator 469 to its first stable state. It can be seen that the alarm signal 453 indicates that there has been a malfunction of the equipment but does not indicate that the alarm has been actuated at the remote location. This is the secondary alarm 500 of FIG. 9.

Lines 461, 462 and 463 are connected to the received signal shifted buses of their respective tones and if a shifted signal is received, AND gates 455, 456, and 457 will generate an output signal. In this example tone B has been shifted in frequency and therefore tone B AND gate 456 will have an output signal which is applied to bistable multivibrator 471. This will cause multivibrator 471 to assume its second stable state. Since there are no A or C signals received, bistable multivibrators 472 and 473 will remain in their first stable state. The output of state 2 of multivibrator 471 will cause lamp 476 to be illuminated and will also cause lamp 479 to be illuminated through OR gate 478. The main alarm 481, 581 of FIG. 9, will be actuated through OR gate 478. Lamp 479 serves as a secondary lamp for lamps 475, 476 and 477 so that if one of these lamps should burn out there will still be a visual indication showing which alarm group has been actuated. Lamps 475, 476, 477 and 479 correspond to lamps 506, 508, 510 and 584 of FIG. 9 respectively. It should be noted that the main alarm 481 and the lamps 475, 476, 477 and 479 indicate that an alarm at the remote location has been actuated. Switches 494, 495 and 496 apply a signal from. the reset input 483 to bistable multivibrators 471, 472 and 473 to reset these multivibrators.

Located on the group panel are reset and test switches 485 and 486 which are mechanically connected. When the switch is moved so that arm 485 is connected to terminal 482 and switch arm 486 is connected to terminal 490 the switch is in the test position. When switch arm 485 is connected to terminal 488 and switch arm 486 is connected to terminal 491 the switch is in the normal operate position. When switch arm 485 is connected to terminal 489 and switch arm 486 is connected to terminal 492 the switch is in the reset position. With the switch in the normal operate position, a signal appearing on of FIG. 2 will not be enabled and the counter 29 of FIG. 2 will not stop even though it has reached a numher having three and only three ones in its registers. The reset bus or the test bus is energized through switch arm 486 connected to either terminal 490 or 492. The signal thus placed on the test bus or the reset bus from input generator 487 through switch arm 486 will notinhibit the AND gate 447 of the display group with which it is associated as the movement of switch arm 486 to the test or reset position disconnects the inhibit input from AND gate 447 through switch 485. The output of the test bus is applied through line 86 to AND gate 69 of FIGURE 2 while the output of the reset bus is applied through line 87 to establish bistable multivibrator 72 of FIGURE 2 in its second stable state as previously described.

The ability to select the desired code group and thus the desired set of alarms by means of the reset and test switch on the control panel can be utilized to select any particular remote receiver for normal interrogation out of its normal sequence. This is done by selecting the desired code group by placing the reset test switch in either the reset or test position. As previously described this will select the appropriate code group but at the same time it will also increase the duration of the transmitted tone group which the receiver will interpret to mean a test or reset request, This can be prevented by opening switch of FIG. 2 prior to selecting the desired tone group. Opening switch 75 prevents the output from ring counter 66 from reaching AND gates 69 and 70. The outputs of these AND gates inhibit AND gate 63 causing the tone transmission time to be increased beyond its normal period. By preventing the output of the second count of the ring counter 66 from reaching AND gates 69 and 70, the AND gates will have no output and the ring counter will run through its normal cycle of operation, interrogating the selected receiver repeatedly until the reset and test switch is placed in its normal position.

The system described will sequentially interrogate remote alarms from a central station. The status of the remote alarms and the remote equipment will be transmitted to the central station where it will be displayed. The remote equipment can be controlled from the central station and any desired station can be interrogated as desired. Transmission security is accomplished by the use of combinations of tones. The transmitting medium can be radio, wire lines or a combination of both.

We claim:

1. A system for indicating at a central location the condition of any one of a plurality of remotely located devices including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting groups of tones from said plurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, means connected to said code means for transmitting said tone groups in sequence with said tones included in each tone group being transmitted simultaneously, terminal means for receiving said tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the remote devices, each of said translator means being responsive to one tone of one of said groups to which said selective means respond and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone, the frequency of which is dependent upon the condition of the remote device coupled to said translator means, means coupled to said selective means for combining said reply tones and simultaneously retransmitting the same to the central location, means at the central location for receiving the retransmitted reply tones, and display means for displaying the condition of the remote devices.

2. A system for indicating at a central location the condition of any one of a plurality of remotely located devices including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting groups of tones from said plurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, means connected to said code means for transmitting said tone groups in sequence, a plurality of terminal means for receiving said tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the remote devices, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone, the frequency of which is dependent upon the condition of the remote device coupled to said translator means, means for generating a function tone dependent upon the condition of said terminal means, means coupled to said selective means for combining said, reply 17 tones and function tones and retransmitting the same to the central location, means at the central location for receiving the retransmitted reply and function tones, and display means for displaying the condition of the remote devices.

3. A system for indicating at a central location the condition of any one of a plurality of remotely located devices including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting groups of tones from said plurality of tones, each of said groups including a difierent combination of tones and less than the total number of said plurality of tones, means connected to said code means for transmitting each of said tone groups for a first time period in sequence with said tones included in each tone group being transmitted simultaneously, terminal means for receiving said tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the remote devices, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone, the frequency of which is dependent upon the condition of the remote device coupled to said translator means, means coupled to said selective means for combining said reply tones and simultaneously retransmitting the same to the central location, means at the central location for receiving the retransmitted reply tones, and display means for displaying the condition of the remote devices, means coupled to said code means to cause said tone groups to be transmitted for a second time period different from said first time period, said selective means including control means responsive to said tone groups transmitted for said second time period to provide controls at the remote devices.

4. A system for indicating at a central location the condition of any one of a plurality of remotely located devices including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting groups of tones from said plurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, means connected to said code means for transmitting said tone groups in sequence with said tones included in each tone group being transmitted simultaneously, terminal means for receiving said tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of trans lator means coupled to each selective means and individually coupled to the remote devices, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone, the frequency of which is dependent upon the condition of the remote device coupled to said translator means, means coupled to said selective means for combining said reply tones and simultaneously retransmitting the same to the central station, means at the central location for receiving the retransmitted reply tones, and display means for displaying the condition of the remote devices, means coupled to said code means whereby said fixed sequence can be changed to select a particularterminal means.

5. A system for indicating at a central location the condition of a plurality of remotely located alarms including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting a fixed sequence of groups of tones from saidplurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, control means and transmitting means, switch means coupled to said control means and responsive thereto to connect said code means to said transmitting means for a first time period, central station receiver means and display means, said switch means being responsive to said control means to connect said code means and said central station receiver means to said display means for a second time period, said first and second time periods being in an alternating sequence, said code means operating to apply different tone groups to said transmitting means during each of said first time periods for simultaneously transmitting said tone included in each tone group until said fixed sequence is completed whereupon said fixed sequence is repeated indefinitely, terminal means for receiving said transmitted tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the alarms, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone the frequency of which is dependent upon the condition of the alarm coupled to said translator means, means coupled to said selective means for combining said reply tones and simultaneously retransmitting the same during said second time period, said central station receiver means acting to receive and separate said retransmitted tones, and said display means acting to display the information contained in said tones.

6. A system for indicating at a central location the condition of a plurality of remotely located alarms including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting a fixed sequence of groups of tones from said plurality of tones, each of said tones including a different combination of tones and less than the total number of said plurality of tones, control means and transmitting means, switch means coupled to said control means and responsive thereto to connect said code means to said transmitting means for a first time period, central station receiving means and display means, said switch means being responsive to said control means to connect said code means and said central station receiver means to said display means for a second time period, said first and second time periods being in an alternating sequence, said code means operating to apply difierent tone groups to said transmitting means during each of said first time periods for simultaneously transmitting said tones included in each tone group until said fixed sequence is completed whereupon said fixed sequence is repeated indefinitely, terminal means for receiving said transmitted tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the alarms, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone the frequency of which is the same as the transmitted tone if the alarm to which said transmitted tone is associated has not been actuated and to generate a tone having a frequency different from said one tone if the alarm has been actuated, means coupled to said selective means for combining said reply 19 tones and simultaneously retransmitting the same during said second time period, said central station receiver means acting to receive and separate said retransmitted tones, and said display means acting to display the information contained in said tones.

7. A system for indicating at a central location the condition of a plurality of remotely located alarms including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting a fixed sequence of groups of tones from said plurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, control means and transmitting means, switch means coupled to said control means and responsive thereto to connect said code means to said transmitting means for a first time period, central station receiver means and display means, said switch means being responsive to said control means to connect said code means and said central station receiver means to said display means for a second time period, said first and second time periods being in an alternating sequence, said code means operating to apply different tone groups to said transmitting means during each of said first time periods for simultaneously transmitting said tones included in each tone group until said fixed sequence is completed whereupon said fixed sequence is repeated indefinitely, terminal means for receiving said transmitted tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the alarms, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone the frequency of which is dependent upon the condition of the alarm coupled to said translator means, means for generating a function tone dependent upon the status of said terminal means and means coupled to said selective means for combining said reply and function tones and simultaneously retransmitting the same during said second time period, said central station receiver means acting to receive and separate said retransmitted tones, and said display means acting to display the information contained in said tones.

8. A system for indicating at a central location the condition of a plurality of remotely located alarms including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting a fixed sequence of groups of tones from said plurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, control means and transmitting means, switch means coupled to said control means and responsive thereto to connect said code means to said transmitting means for a first time period, central station receiver means and display means, said switch means being responsive to said control means to connect said code means and said central station receiver means to said display means for a second time period, said first and second time periods being in an alternating sequence, said code means operating to apply dilferent tone groups to said transmitting means during each of said first time periods until said fixed sequence is completed whereupon said fixed sequence is repeated indefinitely, terminal means for receiving said transmitted tone groups and for retrans- Initting the same including selective means responsive to at least one of said tone groups, a plurality of translator means coupled to each selective means and individually coupled to the alarms each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condition of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone, the frequency of which is dependent upon the condition of the alarm coupled to said translator means, means coupled to said selective means for combining said reply tones and retransmitting the same during said second time period, said central station receiver means acting to receive and separate said retransmitted tones, said display means acting to display the information contained in said tones, means coupled to said code means to cause said tone groups to be transmitted for a third time period ditferent from said first time period, said terminal means being responsive to said tone groups transmitted for said third time period whereby equipment control means located at said terminal means are actuated to control the operation of the remote alarms, said translator means, and said terminal means.

9. A system for indicating at a central location the condition of a plurality of remotely located alarms including in combination, oscillator means for producing a plurality of separate tones, code means connected to said oscillator means for selecting a fixed sequence of groups of tones from said plurality of tones, each of said groups including a different combination of tones and less than the total number of said plurality of tones, control means and transmitting means, switch means coupled to said control means and responsive thereto to connect said code means to said transmitting means for a first time period, central station receiver means and display means, said switch means being responsive to said control means to connect said code means and said central station receiver means to said display means for a second time period, said first and second time periods being in an alternating sequence, said code means operating to apply different tone groups to said transmitting means during each of said first time periods until said fixed sequence is completed whereupon said fixed sequence is repeated indefinitely, terminal means for receiving said transmitted tone groups and for retransmitting the same including selective means responsive to at least one of said tone groups, a plurality of translators means coupled to each selective means and individually coupled to the alarms, each of said translator means being responsive to one tone of one of said groups to which said selective means responds and to the condi tion of the remote device to which said translator means is coupled to generate a reply signal, said selective means being responsive to said reply signal to generate a reply tone the frequency of which is dependent upon the condition of the alarm coupled to said translator means, means coupled to said selective means for combining said reply tones and retransmitting the same during said second time period, said central station receiver means acting to receive and separate said retransmitted tones and said display means acting to display the information contained in said tones, means coupled to said control means whereby said fixed sequence can be changed to select a particular terminal means.

. 10. system for indicating at a central location the condition of remotely located devices, including in combination, means for transmitting a first tone group containing a plurality of tones identifying particular devices with said tones included in said first tone group being transmitted simultaneously, terminal means for receiving said first tone group at a remote location and including means for sensing the condition of the devices selected by the received tones, said terminal means further including means for generating a second tone group having the same number of tones as said first tone group, with the frequency of said tones in said second tone group being determined by the condition of the selected remote devices, said terminal means being responsive to said second tone group to transmit the same to said transmitting means with said tones included in said second tone group being transmitted simultaneously, said transmitting means including display means responsive to said second tone group to indicate the condition of the selected remote devices.

11. A system for indicating at a central location the actuation of a plurality of remotely located alarms, including in combination, means for generating a plurality of tones, means coupled to said generating means for selecting from said plurality of tones, in a fixed sequence, a plurality of first groups of tones, each of said first groups including a difierent combination of tones representing particular alarms and containing less than the total number of said plurality of tones, means coupled to said selecting means for transmitting said first tone groups with said tones included in each of said first tone groups being transmitted simultaneously, terminal means for receiving said first tone groups at a remote location and including means for sensing the actuation of the alarms represented by the received tones, said terminal means further including means for providing second tone groups having the same number of tones as said first tone groups, with the frequency of said tones in said second tone groups being determined by the actuation of the remotely located alarms, said terminal means being responsive to said second tone groups to transmit the same with said tones included in each of said second tone groups being transmitted simultaneously, receiving means including display means for receiving said transmitted second tone groups and displaying the information represented'by the frequency of the tones therein.

References Cited by the Examiner UNITED STATES PATENTS 2,499,225 2/ 1950 Marshall 343-65 2,664,554 12/1953 Doremus et al. 340-163 3,107,340 10/1963 Silliman et a1.

3,131,376 4/1964 Du Vall 340-226 NEIL C. READ, Primary Examiner.

R. M. ANGUS, Assistant Examiner. 

1. A SYSTEM FOR INDICATING AT A CENTRAL LOCATION THE CONDITION OF ANY ONE OF A PLURALITY OF REMOTELY LOCATED DEVICES INCLUDING IN COMBINATION, OSCILLATOR MEANS FOR PRODUCING A PLURALITY OF SEPERATE TONES, CODE MEANS CONNECTED TO SAID OSCILATOR MEANS FOR SELECTING GROUPS OF TONES FROM SAID PLURALITY OF TONES, EACH OF SAID GROUPS INCLUDING A DIFFERENT COMBINATION OF TONES AND LESS THAN THE TOTAL NUMBER OF SAID PLURALITY OF TONES, MEANS CONNECTED TO SAID CODE MEANS FOR TRANSMITTING SAID TONE GROUPS IN SEQUENCE WITH SAID TONES INCLUDED IN EACH TONE GROUP BEING TRANSMITTED SIMULTANEOUSLY, TERMINAL MEANS FOR RECEIVING SAID TONE GROUPS AND FOR RETRANSMITTING THE SAME INCLUDING SELECTIVE MEANS RESPONSIVE TO AT LEAST ONE OF SAID TONE GROUPS, A PLURALITY OF TRANSLATOR MEANS COUPLED TO EACH SELECTIVE MEANS AND INDIVIDUALLY COUPLED TO THE REMOTE DEVICES, EACH OF SAID TRANSLATOR MEANS BEING RESPONSIVE TO ONE TONE OF ONE OF SAID GROUPS TO WHICH SAID SELECTIVE MEANS RESPOND AND TO THE CONDITION OF THE REMOTE DEVICE TO WHICH SAID TRANSLATOR MEANS IS COUPLED TO GENERATE A REPLY SIGNAL, SAID SELECTIVE MEANS BEING RESPONSIVE TO SAID REPLY SIGNAL TO GENERATE A REPLY TONE, THE FREQUENCY OF WHICH IS DEPENDENT UPON THE CONDITION OF THE REMOTE DEVICE COUPLED TO SAID TRANSLATOR MEANS, MEANS COUPLED TO SAID SELECTIVE MEANS FOR COMBINING SAID REPLY TONED AND SIMULTANEOUSLY RETRANSMITTING THE SAME TO THE CENTRAL LOCATION, MEANS AT THE CENTRAL LOCATION FOR RECEIVING THE RETRANSMITTED REPLY TONES, AND DISPLAY MEANS FOR DISPLAYING THE CONDITION OF THE REMOTE DEVICES. 